"Israeli troops jumped onto the boat around 05:30 on Monday," Michalis Grigoropoulos said of the pre-dawn raid by Israeli forces in international waters that killed nine activists and sparked global outrage.

Grigoropoulos was aboard the Eleftheri Mesogeio, smaller than the lead boat, the Mavi Marmara, which Israeli troops had attacked earlier.

"They fired rubber coated bullets, tear gas and then used electroshock weapons on some activists," he told a press conference shortly after Israel deported him and five compatriots to Athens.

"An hour beforehand, at 04:30 local time, we heard gunfire on the Turkish boat Mavi Marmara, the Israelis jumped from helicopters onto the boat," he said.

Israel is still holding hundreds of the 686 passengers they seized and took back to the Israeli port of Ashdod, where Grigoropoulos said he was kept incommunicado, denied access to a lawyer and made to sign papers he did not understand.

'All communication cut'

Grigoropoulos criticised "the wretched detention conditions at Ashdod (where) 500 people were packed in together" saying that "two Greek activists were beaten up" there by Israeli police.

"They made me sign papers on my expulsion, without me knowing what was on the papers because I did not have the right to a translator, a lawyer or to communicate with my family," he said.

The Eleftheri Mesogeio's captain, Zaharias Stilianakis, who was among those returned to Athens, said that "after their assault on the boat, the commandos cut all means of communication".

Another crew member, Aris Papadokostopoulos, said that two of the detained Greeks "were beaten because they refused to give their digital fingerprints".

After storming the boat, the troops then "cut all forms of communication," Papadokostopoulos added.

Around 30 pro-Palestinian Greek activists from the flotilla are still being held in Israel.

Activists who have refused to identify themselves have been taken to an Israeli prison.

Israel has accused activists on the biggest ship in the flotilla of having provoked the confrontation by attacking its soldiers as they boarded the vessel.